Snatch Strap

[Cuppa]

I seem to recall a recommendation in a thread somewhere here that the snatch strap should be rated between 2 & 3 times the weight of your vehicle.

[Mc4by]

Wow, what a comprehensive reply.
Thanks for taking the time to put all that down.

Most aussie sold straps are classed in Kg.
The strap (or kinetic rope) should be 2 to 3 times the weight of the lightest vehicle of either the bogee or the bogger.
Best size for a Patrol is 8,000 to 9,000 Kg (8 is the more common)
Straps are not rated per se as ther are no Standards etc for them so is up to the manuf to call the size.
They are sold as Breaking Strain (B.S.) IE there is no safety factor, no SWL or WLL

Shackles are rated for lifting not winching, snatching etc.
There are various classes and grades but probably the most common are class 5
The 'lifting rating' for a shackle has a safety factor of at least 5 so a 4.5 ton (4,500Kg) has a B.S. in excess of 20,000 Kg (3 times the Snatch strap)
3.2 ton rated shackles are quite OK for non-kinetic recovery of a Patrol but a lot of the fittings are sized for a 4.5 to to be used.
Bow Shackles are for Straps, D shackles are for chain.
Shackles do NOT acheive their rating unles the pin is nipped up IE 'finger tight and back a 1/2 turn does not a 4.5 ton shackle make'.
Not nipping the pin also lends itself to the pin rolling out of the shackle if repeated attempts are made without checking

When rigged for war I carry
1 x 9,000 Snatchie
1 x Kinetic rope 8,000 Kg
1 x 4.5 ton Bow shackle
2 x 3.2 ton Bow shackles
1 x equaliser strap
2 x 2 ton shackles (my snatch strap has anti-recoil webbing straps)
I have another 3.2 ton shackle with my snatch block, winch extensiion and tree protector

[Mc4by]

This is certainly worth a read. Thanks for the link.

I'm not a fan of snatch straps, they seem to place a real jerk on the vehicles.
Take a look at (viking) recovery ropes which are more elastic and much more gentle to use.
http://www.bubbarope.com/professional-recovery-rope

[PeeBee]

I seem to recall a recommendation in a thread somewhere here that the snatch strap should be rated between 2 & 3 times the weight of your vehicle.

Is this recommendation based around getting the required stretch of the strap to generate the recoil action? If so, I am then being led to believe a strap selected with a greater ratio won't give you the same sling shot effect on the basis it has a higher breaking strain and is stiffer/stronger - is this the principle? I am curious as i have just up-sized my 50mm straps of unknown vintage to 75mm / 1000kg breaking strain and wondering if I should have stayed with the 50mm versions - the 50mm units look so much smaller when side by side with the 75mm units. I don't have any idea what my barge weighs when loaded up but suspect close to 3 tonne at a guess, maybe heavier?

[the evil twin]

Is this recommendation based around getting the required stretch of the strap to generate the recoil action? If so, I am then being led to believe a strap selected with a greater ratio won't give you the same sling shot effect on the basis it has a higher breaking strain and is stiffer/stronger - is this the principle?

Pretty much, yeah.

Without getting into in a huge amount of science... the purpose of the strap is to transfer the energy of the momentum from one vehicle to the other in a controlled manner.
If the strap is too stiff the energy is transferred too quickly and then the moving vehicle decelerates with enough energy to smash the drivers teeth together with enough force to crack a wallnut and either the other vehicle launches out like a space shot or the strap or attachement breaks.
If the strap is too light then there may not be enough conserved energy applied before the strap reaches full extension and the moving vehicle looses traction and stops or again, the strap or attachement breaks.

If the strap is more than 3 times the weight then the former is more likely to occur and if the strap is less than 2 times then the latter applies.

The width of the strap is not 100% definitive as the manuf may use different material or thickness but would be a good guide I s'pose

Another point is that if you need to apply in excess of 9 tons of force to get a 3 ton vehicle moving that is sort of similar to trying to tow 9 tons of load (say, 1/2 a semi trailer with no wheels) with a 3 ton vehicle then some pretty average things are going to happen.

I usually dig out the bogged vehicle a reasonable amount and give it a try in low 2nd at about 1200 to 1500 RPM with 2 metres of strap laid down (1/2 a metre by a metre by 1/2 a metre in an S).
If that starts to work then you can go a bit harder or if it works then great, which it usually should.
If the stuck vehicle doesn't move then start digging some more.

[PeeBee]

Pretty much, yeah.

Without getting into in a huge amount of science... the purpose of the strap is to transfer the energy of the momentum from one vehicle to the other in a controlled manner.
If the strap is too stiff the energy is transferred too quickly and then the moving vehicle decelerates with enough energy to smash the drivers teeth together with enough force to crack a wallnut and either the other vehicle launches out like a space shot or the strap or attachement breaks.
If the strap is too light then there may not be enough conserved energy applied before the strap reaches full extension and the moving vehicle looses traction and stops or again, the strap or attachement breaks.

If the strap is more than 3 times the weight then the former is more likely to occur and if the strap is less than 2 times then the latter applies.

The width of the strap is not 100% definitive as the manuf may use different material or thickness but would be a good guide I s'pose

Another point is that if you need to apply in excess of 9 tons of force to get a 3 ton vehicle moving that is sort of similar to trying to tow 9 tons of load (say, 1/2 a semi trailer with no wheels) with a 3 ton vehicle then some pretty average things are going to happen.

I usually dig out the bogged vehicle a reasonable amount and give it a try in low 2nd at about 1200 to 1500 RPM with 2 metres of strap laid down (1/2 a metre by a metre by 1/2 a metre in an S).
If that starts to work then you can go a bit harder or if it works then great, which it usually should.
If the stuck vehicle doesn't move then start digging some more.

Great explanation, very clear and easy to follow the reasoning - thanks.

[Mc4by]

Excellent explanation.... I picked an 8000kg ARB strap so that should be fine.

Pretty much, yeah.

Without getting into in a huge amount of science... the purpose of the strap is to transfer the energy of the momentum from one vehicle to the other in a controlled manner.
If the strap is too stiff the energy is transferred too quickly and then the moving vehicle decelerates with enough energy to smash the drivers teeth together with enough force to crack a wallnut and either the other vehicle launches out like a space shot or the strap or attachement breaks.
If the strap is too light then there may not be enough conserved energy applied before the strap reaches full extension and the moving vehicle looses traction and stops or again, the strap or attachement breaks.

If the strap is more than 3 times the weight then the former is more likely to occur and if the strap is less than 2 times then the latter applies.

The width of the strap is not 100% definitive as the manuf may use different material or thickness but would be a good guide I s'pose

Another point is that if you need to apply in excess of 9 tons of force to get a 3 ton vehicle moving that is sort of similar to trying to tow 9 tons of load (say, 1/2 a semi trailer with no wheels) with a 3 ton vehicle then some pretty average things are going to happen.

I usually dig out the bogged vehicle a reasonable amount and give it a try in low 2nd at about 1200 to 1500 RPM with 2 metres of strap laid down (1/2 a metre by a metre by 1/2 a metre in an S).
If that starts to work then you can go a bit harder or if it works then great, which it usually should.
If the stuck vehicle doesn't move then start digging some more.

[BillsGU]

I think of the snatch strap as a "fuse" in the recovery process. If all turns to poop I would rather break a strap than tear a piece of either vehicle. Bigger is definately not better.

The sort of questions you are asking Mc4by would suggest you may want to look at a 4WD training course or join a 4WD Club and get the training for free.

[Mc4by]

BillsGU I am booked in with Eureka 4WD training for a sand and bush day.
I have made contact with my local club as well and will be attending their next meeting.
I also picked up an ARB 8T snatch strap with shackles for a good price.

I think of the snatch strap as a "fuse" in the recovery process. If all turns to poop I would rather break a strap than tear a piece of either vehicle. Bigger is definately not better.

The sort of questions you are asking Mc4by would suggest you may want to look at a 4WD training course or join a 4WD Club and get the training for free.

[sooty_10]

http://cloud.tapatalk.com/s/580e21fa...nded%20pdf.pdf

Came across this pdf guide on juststraps site.

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